Characterized by a greater, faster and more specific antibody response alter repeated immunization, immunological memory is still poorly understood and yet widely manipulated for the prevention of disease. The overall goal of the proposed research is to characterize the means by which a B-cell memory response is generated from naive B-cells and to define the requirements for the maintenance of such responses. To elucidate the elements of B-cell memory, a novel experimental system in mice was generated. These mice (monoclonal B-T mice) have a knock-in heavy-chain gene, a transgenic lambda light chain and a transgenic T helper T-cell receptor. Because they are engineered in a V(D)J recombinase-negative background, the primary antibody repertoire is monoclonal and can be diversified in response to immunization. In this way, by immunization with a hapten-carrier conjugate, a memory response and memory B-cells are generated. In one variant of the mouse models, the immunoglobulin expression by the B-cells will be regulated by the tet repressor system (Inducible immunoglobulin mice). In these mice, generation of B-cells memory will be studied under various conditions of surface Ig expression by the B-cells. One goal of these studies is to determine whether memory B-cells in addition to plasma cells can be identified after a primary response and whether memory B-cells have an activated or resting phenotype. Another goal is to determine whether expression surface Ig on B-cells will affect cell differentiation to effector-plasma cell vs. memory cell upon engagement by antigen. These goals will be achieved by analysis of the antigen specific Ig titer and by analysis of somatic hypermutation of the heavy-chain V exons following immunization with the cognate antigen.